In the equipment of a house for the use of electricity, the wiring, together with distributing panel, the various outlets, receptacles, switches, and other appliances that make up the system, is of more than passing consequence. In the construction of the electric system it is important that the wires and their installation be done in a manner to meet every contingency.

The following descriptions for electric house wiring were taken from a set of specifications published by the Bryant Electric Co. as applying to buildings of wood frame construction. The specifications serve as explanations for the appliances required in an ordinary dwelling. The specifications are for the least expensive form of good practice in wiring for frame buildings. They would not be permitted in large cities where further protection from fire is required and where more rigid rules are demanded by the Board of Fire Underwriters.

1. System

The circuit wiring shall be installed as a two-wire direct current or alternating system. Not more than 16 outlets or a maximum of 660 watts shall be placed on any one circuit, allowing 110 watts for each baseboard plug connection or extension outlet and 55 watts for each 16 candlepower lamp indicated at the various wall and ceiling outlets on plans. All wiring shall be installed as a concealed knob-and-tube system.

The type of wiring is designated as a two-wire direct or alternating current system in order that there shall be no doubt as to the method of wiring to be used. There are other methods that might be employed that need not be discussed here.

The 16 outlets mentioned are intended to cover all lamps or plug attachments that are to be used for heaters, fans, motors, or any other electric device. The 660 watts at 110 volts pressure will require 6 amperes in the main wires of the circuit, which is the maximum current the wires are intended to carry. This does not mean that 110-watt lamps might not be used but that no single circuit shall carry lamps that will aggregate more than 660 watts.

The concealed knob-and-tube system mentioned is illustrated in Figs. 263 and 264, in which the wires which pass through joists and studding are to be insulated by porcelain tubes and those wires which lay parallel to these members are to be fastened to porcelain knobs which are secured by screws to the wood pieces to prevent any possibility of coming into contact with electric conducting materials.

2. Outlets

At each and every switch, wall, ceiling, receptacle or other outlet shown on plans, install a metal outlet box of a style most suitable for the purpose of the outlet. All outlet boxes must be rigidly secured in place by approved method and those intended for fixtures shall be provided with a fixture stud, or in the case of large fixtures, a hanger to furnish support independent of the outlet box.

Outlet Boxes

For the safe and convenient accommodation of switches, receptacles or other connections in the walls and ceilings of a building, outlet boxes are used as a means of securing the wire terminals to the receptacles. These boxes are made in a number of forms for general application. One style is shown in Fig. 265. The boxes are made of sheet steel and arranged to be secured in place with screws. The box is further provided with screw fastenings to which the switch or receptacle may be firmly attached.

3. Installation of Wires, Etc

All wires shall be rigidly supported on porcelain insulators which separate the wire at least 1 inch from the surface wired over. Wires passing through floors, studding, etc., shall be protected with porcelain tubes, and where wires pass vertically through bottom plates, bridging, etc., of partitions, an extra tube shall be used to protect wires from plaster droppings. Wires must be supported at least every 4 feet and where near gas or water pipes extra supports shall be used. All porcelain material shall be non-absorptive and broken or damaged pieces must be replaced. Tubes shall be of sufficient length to bush entire length of hole. At outlets the wires shall be protected by flexible tubing, the same to be continuous from nearest wire support to inside of outlet box. Wires installed in masonry work shall be protected by approved rigid iron conduit which shall be continuous from outlet to outlet.

Fig. 263.   Manner of securing wires by the knob and tube system for ceiling outlets.

Fig. 263. - Manner of securing wires by the knob-and-tube system for ceiling outlets.

Fig. 264.   This shows the knob and tube system of securing the wires in partitions and the manner of fastening metal

Fig. 264. - This shows the knob-and-tube system of securing the wires in partitions and the manner of fastening metal "cut out" boxes; for switch, attachments, plugs, etc.

The method and reasons for supporting the wires described above are as have already been mentioned under item 1. The reason for extra supports near gas pipes and water pipes is as a precaution against the possibility of short-circuiting.

4. Conductors

Conductors shall be continuous from outlet to outlet and no splices shall be made except in outlet boxes. No wire smaller than No. 14 B. & S. gage shall be used and for all circuits of 100 feet or longer, No. 12, B. & S. gage or larger shall be used. All conductors of No. 8 B. & S. gage or larger shall be stranded. Wires shall be of sufficient length at outlets to make connection to apparatus without straining connections. Splices shall be made both mechanically and electrically perfect, and the proper thickness of rubber and friction tape shall be then applied.

Continuous conductors are required because of the possibility of defects in the joints of spliced wire.

5. Position of Outlets

Unless otherwise indicated or directed, plug receptacles shall be located just above baseboard; wall brackets, 5 feet above finished floor in bedrooms, and 5 feet 6 inches in all other rooms; wall switches, 4 feet above finished floors. All outlets shall be centered with regard to panelling, furring, trim, etc., and any outlet which is improperly located on account of above conditions must be corrected at the contractor's expense. All outlets must be set plumb and extend to finish of wall, ceiling or floor, as the case may be, without projecting beyond same.

6. Materials

All materials used in carrying out these specifications shall be acceptable to the National Board of Fire Underwriters and to the local department having jurisdiction. Where the make or brand is specified or where the expression "equal to" is used, the contractor must notify the architect of the make or brand to be used and receive his approval before any of said material is installed. Where a particular brand or make is distinctly specified, no substitution will be permitted.

Fig. 265.   Outlet box.

Fig. 265. - Outlet box.

7. Grade of Wire

The insulation of all conductors shall be rubber, with protecting braids, which shall be N.E.C. Standard (National Electrical Code Standard).

8. Outlet Boxes

Outlet boxes shall be standard pressed steel, knockout type and shall be enameled.

9. Local Switches

Local wall switches shall be two-button flush type completely enclosed in a box of non-breakable insulating material with brass beveled-edge cover plate finished to match surrounding hardware.

Fig. 269 shows the various forms and grades of switches that there are on the market. The screws which attach the plate to the switch enter bushings that are under spring tension thereby preventing defacement of the plate by overtightening of the screws. Single-pole is to be used where the load will not be in excess of 660 watts; double-pole to be used where the load is more then 660 watts or where for any other reason it is desirable to break the current at both wires. Three-point switches are to be used when a light'or group of lights is to be controlled, as hall lights that may be lighted or extinguished, from either the top or at the bottom of a stairway. Four-point switches are to be used between and two, three-point switches to control additional lights. Where two or more switches are placed together an approved gang plate is to be provided which designates the use of each switch. Where indicated on the plan, clothes closets shall be equipped with automatic door switch to connect the light when the door is open.

10. Pilot Lights

Switches controlling cellar, attic and porch lights shall have pilot lamp in parallel on the load side of the switch. The switch in Fig. 3 requires for its installation a two-gang outlet box. The ruby bull's-eye which covers the lamp is practically flush, extending from the wall no further than the buttons of the switch.

Pilot lights are intended to indicate the operation of other lights or apparatus that cannot be directly observed.

The term bull's-eye applies to a colored-glass button covering a miniature lamp which burns whenever a light is used which is apt to be forgotten and allowed to burn for a longer time than necessary.

11. Plug Receptacles

Plug receptacles shall be of the disappearing-door type, with beveled-edge brass cover plate finished to match surrounding hardware (see Fig. 266). In this receptacle the doors are pushed inward by the insertion of the plug and upon its withdrawal close automatically, effectually excluding dirt and concealing the live terminals. It is the latest and best plug receptacle obtainable.

Plug receptacles are the attachments for the terminal pieces of plugs, which temporarily connect portable lamps, electric fans or other devices, they are made in many forms.

12. Wall and Ceiling Sockets

One-light ceiling receptacles shall be of a type to fit standard 3 1/4-inch or 4-inch outlet boxes. Wall sockets shall be of the insulated base type. Sockets in cellars shall be made entirely of porcelain and of the pull type. All lamp sockets used in fulfilling these specifications shall have an approved rating of 660 watts, 250 volts.

13. Drop Lights

Drop lights shall consist of the necessary length of reinforced cord supported by an insulated rosette with brass base and cover; the latter to cover 4-inch outlet box, and furnished with a key socket complete with a 2 1/4-inch shade-holder. Each drop cord shall have an adjuster.

14. Heater Switch, Pilot and Receptacle

Heating device outlets shall be equipped with combination of switch, pilot light and receptacle with plug and spare pilot lamp.

15. Service Switch

The service-entrance switch shall be 30 amperes, porcelain base with connections for plug fuses.